Pressure fluid motor



Oct. 28, 1941. J c, CURTIS ET AL 2,260,300

PRESSURE FLUID MOTOR Filed NOV. 1, 1940 32 lfivenions': 36 Jbhn L. LurZv'd'. 1 5 26 32 Charla}? UJgood, 62

Patented Oct. 28, 1941 PRESSURE FLUID MOTOR John 0. Curtis and Charles F. Osgood, Claremont,

. N. H., assignors to Sull ivan Machinery Company, a corporation of Massachusetts Application November 1, 1940, Serial No. 363,925

15 Claims.

This invention relates to pressure fluid motors, and more particularly to improvements in the fluid distributing valve mechanism of a pressure fluid motor of the reciprocating piston type.

An object of the present invention is to provide an improved pressure fluid motor. Another object is to provide an improved fluid distributing valve mechanism for a pressure fluid motor. Yet another object is to provide an improved valve mechanism of the double valve type. A still further object is to provide an improved double valve mechanism wherein the fluid distributing valves are separated by an intermediate sleeve which improves the sealing of the valves to prevent fluid leakage. Another object is to provide an improved double valve mechanism wherein identical fluid distributing valves are employed, the valves having like operating functions and being interchangeable without afiecting their operating functions. A still further object is to provide an improved double valve mechanism wherein machining and finishing of the valves are simplified while sealing to prevent leakage of fluid pastthe valves is improved. Still another object is to provide an improved sleeve interposed between a pair of relatively movable fluid distributing valves wherein sealing of the valves is improved, the sleeve also serving as a valve actuating and holding element engageable with the valves whereby when one valve moves toward open position it imparts through the sleeve a force for shifting the other valve toward and holding the same in its closed position. These and other objects and advantages of the invention will, however, hereinafter more fully appear.

In the accompanying drawing there is shown for purposes of illustration one form which the invention may assume in practice.

In this drawing:

Fig. 1 is a view in longitudinal vertical section through a pressure fluid motor embodying a valve mechanism constructed in accordance with an illustrative embodiment of the invention.

Figs. 2 and 3 are views similar to Fig. 1, showing parts in diflerent positions.

Fig. 4 is an enlarged fragmentary sectional view taken on the plane of Fig. 1, illustrating the improved valve mechanism.

Fig. 5 is a perspective view of the intermediate sleeve.

In this illustrative embodiment of the invention .I generally designates a pressure fluid mo-- tor which may be of the same general type as that disclosed in a copending application of J. C.

Curtis, Serial No. 315,786, filed January 26,.1940, now matured into Patent No. 2,224,861, granted Dec. 17, 1940.

The pressure fluid motor disclosed herein comprises a motor cylinder 2 having a bore 3 containing a reciprocatory motor piston 4. The motor. cylinder has a rear head 5 and a front head 6, and the motor piston has a piston head I slidably fitting the cylinder bore and a forwardly projecting cylindric portion 8 guided in the bore of a sleeve 9 suitably secured within the front motor head. Also formed in the motor cylinder and arranged in axial alinement with the cylinder bore at the rear end of the latter is an enlarged bore I0, and the rear cylinder head has a cylindric portion fitted within the bore It] in the manner shown in Fig. 1. Also arranged in the bore I0 is a cylindric valve box ll having acylindric valve box cover l2 abutting its rear face. An annular member I3 is also arranged in the bore l0 intermediate'the valve box cover I2 and anannular member l4. A rear head block I5 abuts the rear'face of the member M for clamping the parts 5, ll, [2 and I3 in position within the. bore l0, anda suitable dowel pin is provided for holding the parts in proper relation. The valve box .H has alined, end, valve-receiving bores I6 and I1 connected by a reduced bore l8 in an intermediate partition IS. The rear head 5 has a rearwardly projecting, cylindric, sleevelike extension 20 fitting tightly within a bore 2| in the valve'box cover ,l2. The walls of the bores l5 and I1 and the exterior surface of the extension 20'cooperate to provide the inner and outer concentric walls of apair of valve chambers 22 and 23, and the opposite surfaces of the partition l9 and the inwardly facing surfaces of the cylinder head 5 and the valve box cover l2 provide the inner and outer end walls of the valve chambers. Arranged in the valve chambers is a pair of relatively movable, fluid actuated, fluid distributing valves 24 and 25 respectively controlling the flow of pressure fluid to the opposite ends of the cylinderv bore. Interposed between the valves is a cylindric sleeve 26 slidingly fitting at its exterior periphery the bore la in the partition l9. The valves 24 and 25 are identical in design and shape andhave like operating functions so that they may be interchanged without affecting their op erating functions. The valves have sleevelike bodies 21 and 28 slidingly telescopically fitting the bore of the sleeve 26, and projecting outwardly from the valve bodies are annular flanges 20 and 30 respectively, these valve flanges slidternal valve'flanges 3l and 32 that the flow of pressure fluid-past the valves ingly fitting the valve box bores l6 and I1. Projecting inwardly of the valve bodies are internal annular flanges 3| and 32' which respectively cooperate with an external cylindric portion 33 integral with the valve box cover and an external cylindric portion 34 integral with the rear cylinder head as shortly explained. Within the valves and intermediate sleeve is an internal fluid supply chamber 35, and the internal valve flanges 3i .and 32 and the cylindric portions 33 and 34 cooperate to provide relatively restricted or metered flow of pressure fluid from the internal supply chamber 35 past the valves to the opposite ends of the motor cylinder bore. The remote end faces of the sleevelike valve bodies21' and :28 provide annular end-seating surfaces 36 and 31 respectively. the former being adapted to seat:

against the front face of the valve and the latter against the rear face ofthe rear cylinder head. Formed on the front face of the valve box cover l2 and communicating with the rear valve chamber 22 is an annular recess 38 connectedby a port 39 with a fluid distributing passage 4il', the latter in turn being connected by a port 4| with the front end of the cylinder bore.

Fluid distributing passages 42 in the rear cylinder head, connect the front valve chamber 23 directly with the rear end of the cylinder bore.

The means for supplying pressure fluid to the fluid supply chamber 35 within the valves and intermediate sleeve comprises a throttle valve 45 arranged in a transverse bore in the rear head block l5 and having an internal fluid supply chamber 46 connectible by a port 41 in the valve with'apassage 48 in turn communicating with a chamber 49inthe member I4. Pressure fluid may be conducted from the chamber 49through passages 50 and the bore of the member I 3 to passages. 5| vinthe valve box cover. 1 Passages 5| communicate with an annularrecess 52 in turn corlnected'to an annular passage 53 surrounding therearhead extension and formed within the" cylindric portion 33. municates directly with the fluid supply chamber 35 within the valves and intermediate sleeve. The ivalve'chambers at the inner adjacentsides of theiexternal valve flanges 29 and are con nected'jto the" cylinder borethrough throwing passages 54 a'nd55 respectively, which are respectively connected to thevalve box bores through'ports56 and 5! and to the cylinder bore through ports 58 and'59. Formed inthe walls of. the cylinder bore substantially midway be tween its 'endsis an annular, exhaust groove 60. connected dir'ectly to atmosphere through an P exhaust port 6|. "The .ports 58 and 59 of the valve-throwing passages communicate with the cylinder bore at points spaced longitudinally of the cylinder bore at the opposite sides of'the exhaust groove '60 inithe manner shown. Pressureflu-id may flow from theinternal fluid supply chamber past restricted clearance spaces 62 and 63 at the inner peripheral edges of the into the fluiddistributing passages and 42 is always maintained-constant irrespective of any wear of the valves; the valves being guided solely attheir: exterior peripheries. The intermediate sleeve26'slidinglyofltting the bore I8 of the par- 1 titio'n';'I -9-;andthe exterior surfaces of the sleeve- 1 like valve bodies 27 and 28 providesa fluid-tight seal -t9; prevent fluid leakage past the valves while enabling location of the valves in close adjacency. By making the valves identical, the

The passage 53 com respectively so box cover v so": that there is an external same may be readily assembled and machining sure fluid motor will be clearly apparent from the" description given. When the parts are in the position shown in Fig. 1, pressure fluid may flowfrom the supply chamber 35 within the valves and intermediate sleeve 26, through the restricted clearance space 63, through the valve chamber 23 past the front face of the front valve 25 and through the fluid distributing passages 42 to the rear end of the cylinder bore at the rear side of the motor piston, the pressure fluid i acting on the rear pressure area of the piston head to move the piston forwardly to effect its working stroke. Concurrently, the front end of the'cylinder' bore at the front end of the piston head is connected to exhaust through the exhaust' groove and exhaust passage 6|. The front valve 25 is at this time held in its rearward position by the pressurefluid acting on the effective, front pressure area of the valve, and the latter due to its abutting engagement with the .sleeve26, acts, through the intermediate sleeve,

to hold the rear valve 24 in its closed position against the front face of the valve box cover.

' As the motor piston moves forwardly from the position shown in Fig. 1,' the leading edge of the pi ston head first overruns the port 59 of the and'thereafter the leading edge-of the piston head overruns the exhaust groove BD the'reby cutting off communication of the front end; of the cylinder bore with exhaust; and upon continued forward'piston'move- V men-t theleading edge of the piston head overruns-the port 58 of the throwingpassage 54. Thereafter thefollowing edge of the piston head uncovers the port '59 of the throwing passage 55, admittin'gfpressure-fluid from the rear end of the cylinder bore through the throwing passage and port 51to the valve box bore l1 at the rear sideof the external valve flange 30 of the front valve 25 Due to the restriction at 63 between theintern al pressure chamber 35 and the valve box bore [1 at the front side of the front valve free flow of fluid from the 25- andthe relatively front end of the valve box bore l! to the rear end of the cylinder bore through the passages 42, the pressure of the fluid at the rear side of the internal valve flange 32 is substantially greater than the pressure in the valve box boreat the front side of the valve, so that when throwing pressure is admitted the effective pressure acting on the external valve flange 30 is sufli cient to throw the front valve forwardly from the position shown in Fig. 1 to the position shown in Fig. 2. When the front valve 25 moves to its. foremost position shown in Fig; 2, the annular end-seating surface 31 thereon seats against the rear face of the rear cylinder head 5, but the rear valve 24 remains momentarily seated against the front face ofthe valve boxcover. in its rearmost closed position by the pressure of thefluid' acting on the then exposed forward to the throwing passage 55 The rear valve is maintained end pressure-area of the sleeve 26 which abuts the rear valve. When the valves are both held closed, as shown in Fig. 2, flow of pressure fluid to both ends of the cylinder bore is momentarily concurrently completely out off and forward front end ofthe intermediate sleeve'26 are connected to atmosphere. The compression pressure builtup by the motor piston within the front end of the cylinder bore transmitted through port 41, passage 40 and port 33 to the effective rear pressure area of the external flange of the rear valve24 thenv acts to throw immediately the latter from the position shown in Fig. 2 to its position shown in Fig. 3. It will be evident, however, that if the pressure in the rear end of the cylinder, in passage 55 etc., drops low enough, due to expansion, before the exhaust groove is uncovered (as may easily be caused to take place by appropriate design) valve throwing concurrent with or slightly prior to rear end release, can be secured. When the valves 24 and are in the position shown in Fig. 3, pressure fluid may flow from the supply chamber within the valves and intermediate sleeve through the restricted clearance space 62, through the valve box bore I6, past the rear face of the rear valve 24 and through recess 38, port 39, passage and port 4| to the front end of the cylinder bore at the front side ofthe iston head, the pressure fluid acting on the forward pressure area of the piston head to move the piston rearwardly to effect its return stroke. Concurrently, the rear end of the cylinder bore at the rear side of the piston head is connected to exhaust through the exhaust groove 60 and exhaust passage 6!. The rear valve 24 is at that time held in its forward position by the pressure fluid acting on the rear pressure area of the valve, and the latter, due to its abutting engagement with the sleeve 26, acts, through the sleeve, to maintain the front valve in its closed position against the rear face of the rear cylinder head 5. As the motor piston moves rearwardly from the position shown in Fig. 3, the leading edge of the piston head first overruns the exhaust groove 60, thereby cutting off communication of the rear end of the cylinder bore with'exhaust; and upon continued rearward piston movement the leading edge of the piston head overruns the port 59 of the throwing passage 55, and thereafter the following edge of the piston head uncovers the port 58 of the throwing passage 54, admitting pressure from the front end of the cylinder bore through the throwing passage 54 and port 56 to the valve box bore 16 at the forward side of the external flange 29 of the rear valve 24. Due to the restriction at 62 between the internal pressure chamber 35 and the valve box bore H5 at the rear side of the rear valve and the relatively free flow of fluid from the rear end of the valve box bore to the front end of the cylinder bore through the passage 40, the pressure of the fluid at the forward side of the internal valve flange 3| is substantially greater than that in the valve box bore at the rear side of the rear valve, so that when throwing pressure is admitted to the valve box bore l6 at the front side of the external valve flange 29 the effective pressure is suflicient to throw the rear valve rearwardly from the position shown in Fig. 3 to the initial position shown in Fig. 1. When the rear valve 24 is in its rearmost position shown in Fig. 1, the annular end-seating surface 36 thereon is. seated against the front face of the valve box cover while the front valve 25 is maintained seated against the rear face of the rear cylinder head by the pressure of the fluid acting on the then exposed rear pressure area of the sleeve 26 which abuttingly engages the front valve. .The front valve 25 will be opened by compression pressure acting through the passages 42 at least by the time piston head 1 in its rearward movement uncovers'the exhaust groove 60, at which time, as will be evident, the valveholding force provided by the action of pressure fluid transmitted from the front end of the cylinder bore upon the rear end of the sleeve 26 will be relieved. When the front valve 25 is opened, it returnsto the position shown in Figs. 1 and 4, andacts to -hold the rear valve 24 closed by pressure transmitted through the sleeve 26. The sequence of events above described is rapidly repeated during normal operation of the motor.

As a result of this invention it will be noted that an improved pressure fluid motor is provided having improved fluid distribution means wherebypressure fluid is distributed to the motor cylinder in an improved and more effective manner. It will further be evident that by the provision of an improved valve mechanism of the doublevalve type having an intermediate sleeve engaging both valves, not only is sealing of the valves to prevent fluid leakage improved, but also machining and finishing of the parts are simplified. It will further be noted that by the provision of a double valve mechanism wherein identical valves having: like operating functions are employed, the valves may be interchanged without affecting their operating functions. Other uses and advantages of the improved pressure fluid motor will be clearly apparent to those skilled in theart. 1

While there is in this application specifically described one form which the invention may assume in'practice, it will be understood that this form of the same is shown for purposes of illustration and that the invention may be modified and embodied in various other forms without departing from its spirit or the scope of the appended claims.

What we claim as new by Letters Patent 1. In combination, in a motor, a cylinder, a piston reciprocable in said cylinder, and fluid and desire to secure distribution means for the motor including means providing a valve chest, fluid distributing passages leading from said valve chest to the opposite ends of said cylinder, a pair of fluid distributing valves arranged within said valve chest and an intermediate sleevelike member separating said valves and adapted to abut the latter in certain positions thereof, said valves being movable relative to each other and said sleevelike member, and said valves and sleevelike member being movable relative to the valve chest, said valves and sleevelike member cooperating with the valve chest in one position of 'said'valves to provide internally of said valves and sleevelik member a chamber sealed from communication with said cylinder through said passages, and means. for delivering motive. fluid to said internal chamber for distribution therefrom under the control of said valves through said passages to the opposite ends of said cylinder.

2. In combination, in a motor, a cylinder, a piston reciprocable in said cylinder, and fluid distribution means for the motor including means providing a valve chest, fluid distributing passages leading from said valve chest to the opposite ends of said cylinder, a pair of fluid di s tributing valves arranged in said valve chest and an intermediate sleevelike member separating said valves and with which the latter are adapted to abut in certain positions thereof, said valves movable relative to each other and said sleevelike member, and said valves and sleevelike member movable relative to said valve chest, an internal fluid supply chamber provided within said valves and sleevelike member, said valves controlling the flow of pressure fluid from said internal fluid supply chamber to'said passages,

and means for effecting throwing of said valves including pressure areas on each of said valves to which fluid is delivered to effect valve closure and means under the control of said piston for delivering fluid to and venting fluid from said pressure areas. I j

3. A pressure'fluid motor comprising, in combination, a cylinder, a piston therein, and fluid distribution means for the motor including passage means for supplying operatingfluid to the opposite ends of said cylinder at the opposite sides of said piston respectively, an operating fluid supply, fluid distributing valve means including a pair of relatively movable valves and an intermediate sleevelike member separating said valves, said valves abuttingly engageable with said sleevelike member in positions wherein one valve exerts a pressure on said sleevelike member to hold the other valve stationary, and said valves respectively "controlling the flow ofoperating fluid to the opposite ends of said cylinder by controlling the communication of said passage means with said fluid supply, and valve-throwing means for subjecting said valves to valve-throwing pressures tomove said valves into their diiferent operating positions, said valves in certain positions thereof momentarily completely cutting off communication of'both of said passage means with said fluid supply.

4. A pressure fluid motor comprising, in com bination, a cylinder, a piston therein, and fluid distribution means "for the motor including passage means for supplying operating fluid to the opposite ends of the cylinder at the opposite sides of the piston respectively,an operating fluid supply, fluid distributing valve means in-, cluding a pair of relatively movable valves and an intermediate sleevelike member separating said valves, said valves movable into abutting engagement with said sleevelike member and respectively controlling the flow of operating fluid to the opposite ends ,of said cylinder by controlling the communication of said passage means with said fluid supply, and valve-throwing means for subjecting said valves to valvethrowing pressures to move said valves into their diiTerent operating positions, one of said valves being held in closed position by the other valve abuttingly acting on said sleevelike member, and'said valves in certain positions when one of them is out of abutting engagement with said sleevelike member momentarily concurrently completely'cutting off communication of both of said passage means with said fluid supply,

. fluid supply.

5. A pressure fluid motor comprising in combination, a cylinder, a piston therein, and fluid distribution means for the motor including passage means for supplying operating fluid to the opposite ends of said cylinder at the opposite of said cylinder by controlling the communication of said passage means with said fluid supply,

and valve-throwing means for subjecting said,

valves to valve-throwing pressures to move said valves into their difierent operating positions,

said valves adapted abuttingly to engage said,

sleevelike member and being movable toward pletely cutting off communication of both of said passage means with said fluid supply and each, through said sleevelike member, exerting in its full open position a force for holding the other valve closed.

6- A. pressure fluid motor comprising, in combination, a cylinder, a piston therein, and fluid distribution means for the motor including passage means for supplying operating fluid to-the opposite ends of said cylinder at the opposite sides of said piston respectively, an operating fluid supply, fluid distributing valve means including a pair of relatively movable valves and an,

intermediate sleevelike member separating said valves, said valves movable into abutting engagement with said sleevelike member and respec-. tively controlling the flow of operating fluid to the opposite ends of said cylinder, for controlling the communication of said passage means with said fluid supply, and valve-throwing means for subjecting said. valvesrtol valve-throwing pressures to move said valve into their different operating positions, said valves upon relative movement toward one another abuttingly engageable with said sleevelike member and each of said valves upon relative movement from the other movable out of such abutting engagement and said valves when in their positions away from one another with meet them out of abutting relation with said sleevelike member momentar ily concurrently completely cutting oiT communication of both of said passage means with said 7. In a pressure, fluid motor, the combination comprising a cylinder having a bore, a piston reciprocable in said cylinder bore, and fluid distribution means for supplying pressure fluidto and exhausting fluid from said cylinder to effect reciprocation of said piston comprising means pro-.

viding a valve chest, a pair of'relatively movable annular fluid distributing valves and a cooperating intermediate sleevelike member separating said valves, said valves movable into and out of abutting relation with said sleevelike member, said valves and sleevelike member cooperating to divide said valve chest into inner and outer spacesand end pressure spaces at the remote ends of said valves, means for effecting movement of said valves relative to each other and said sleevelike member into their difierent nor mal operating positions in'said valve chest, means for supplying motive pressure fluid, to one of said inner and outer spaces, said valve-movementeifecting means including; means for supplying pressure fluid to and exhausting fluid from others.

spaces respectively 'of said inner and outer pressure spaces for eifecting movement of said valves into certain of their operating positions, and means providing fluid supply passages for connecting said end pressure with the opposite ends of said cylinderjbore,,said' valves. respectively controlling the flow of pressure fiuidfrom the pressure fluid supply space through said end pressure spaces to said supply passages.

8. In a pressure fluid motor, the combination comprising a cylinder having a bore, a'piston reciprocable in said cylinder bore, and fluid distribution means for supplying pressure fluid to and exhausting fluid from said cylinder bore to eflect reciprocation of said piston comprising means providing a valve chest, a pair of relatively movable fluid distributing valves movably mounted in said valve chest and an intermediate annular member separating said valves, said valves and annular member arranged in coaxial relation and having open centers, and the pressure fluid flowing to one end of said cylinder bore through the open centers of said valves and annular member, means for effecting movement of said valves relative to one another and said annular member into their different normal operating positions in said valve chest, and means providing supply passages leading from the opposite ends of said valve chest respectively to the opposite ends of said cylinder bore, said valves respectively con trolling the flow of pressure fluid through the ends of said valve chest to said supply passages.

9. In a pressure fluid motor, the combination comprising a cylinder, 2. piston reciprocable in said cylinder, and fluid distribution means for the motor including means providing a valve chest, a pair of relatively movable valves and an intermediate sleevelike member separating saic' valves and with which the latter are movable into abutting engagement, one valve being adapted to exert, through said sleevelike member, a pressure tending to hold the other valve closed, fluid dis tributing passages leading from said valve chest to the opposite ends of said cylinder, a pressure fluid supply, s'aid valves controlling the flow of fluid from said supply to said passages, and means for effecting throwing of said valves and sleevelike member into their different operating positions.

10. In a pressure fluid motor, the combination comprising a cylinder, a piston reciprocable in said cylinder, and fluid distribution means for the motor including means providing a valve chest, a pairof relatively movable valves and an intermediate sleevelike member separating said valves and with which the latter are movable into abutting engagement, one valve being adapted to ex ert, through said sleevelike member, a pressure tending to hold the other valve closed, fluid distributing passages leading from said valve chest to the opposite ends of said cylinder, a pressure fluid supply, said valves controlling the flow of fluid from said supply to said passages, and means for effecting throwing of said valves and sleevelike member into their diflerent operating positions, said sleevelike member having end pressure areas adapted when exposed to be subjected to pressure fluid to hold the valve with which it abuts in closed position.

11. In a pressure fluid motor. the combination comprising a cylinder, a piston reciprocable in said cylinder, and fluid distribution means for the motor including means providing a valve chest, a pair of relatively movable valves and anintermediate sleevelike member separating said ;ber,ja pressure tending to hold the other valve closed, fillid distributing passages leading from said valve chest to the opposite ends of said cylinder, a pressure fluid supply, said valves controlling the flow of fluid from said supply to said passages, and means for efiecting throwing of said valves and sleevelike member into their different operating positions.

12. A pressure fluid motor comprising, in combination, a cylinder, a piston reciprocable therein, and fluid distribution means for the motor comprising means providing a valve chest, a pair of relatively movable fluid distributing valves and an intermediate element separating said valves and with which the latter are adapted to abut, said valves and intermediate element being movably mounted in said valve chest, one valve in one position adapted to exert, through said intermediate element, a force tending to hold the other valve closed, fluid distributing passage means controlled by said valves for conductingmotive fluid to the opposite ends oi. said cylinder, and valve-throwing means controlled by said piston for throwing said valves and intermediate element into their different operating positions.

13. A pressure fluid motor comprising, in combination, a cylinder, a piston reciprocable therein, and fluid distribution means for the motor comprising means providing a valve chest, a pair of relatively movable fluid distributing valves and an intermediate element separating said valves and with which the latter are adapted to abut, said valves and intermediate element being movably mounted in said valve chest and arranged in sliding telescopic relation, one valve in one position adapted to exert, through said intermediate element, a force tending to hold the other valve closed, fluid distributing passage means controlled by said valves for conducting motive fluid to the opposite ends of said cylinder, and valve-throwing means controlled by said piston for throwing said valves and intermediate element into their different operating positions.

14. A pressure fluid motor comprising, in combination, a cylinder, a piston reciprooable therein, and fluid distribution means for the motor comprising means providing a valve chest, a pair of relatively movable fluid distributing valves and an intermediate element separating said valves and with which the latter are adapted to abut, said valves and element being movably mounted in said valve chest, one valve in one position adapted to exert, through said intermediate element, a force tending to hold the other valve closed, fluid distributing passage means controlled by said valves for conducting motive fluid to the opposite ends of said cylinder, and valvethrowing means controlled by said piston for throwing said valves and intermediate element into their different operating positions, said intermediate element having pressure areas adapted, when exposed, to be subjected to pressure fluid to hold the valve with which it abuts in closed position.

15. A pressure fluid motor comprising, in combination, a cylinder, a piston reciprocable in said cylinder, and fluid distribution means for the motor comprising means forming a valve chest, passages respectively adapted to transmit operating medium from said valve chest to the opposite endsof said cylinder and a pair of relatively ments, said valve elements each when infull movable-valve elements and an intermediate eIeopen position exerting on the other a holding mentseparatingsaid valve elements, said several pressure, and said intermediate element when elements arranged in said valve chest, said fluid said valve elements are both closed exerting on distribution meansfurther' including means for 5 the latter in turn intermittent holding pressures.

transmitting pressure variations-in the cylinder 'JOHN C. CURTIS.

to said valve chest t'o act onsaid several ele- CHARLES F. OSGOOD. 

